let _Vue = null

export default class VueRouter {
    constructor(options) {
        this.options = options
        this.routeMap = {}
        this.data = _Vue.observable({
            currentRoute: '/'
        })
    }

    // vue 为 Vue构造函数
    // options 为可选的选项对象
    static install(Vue, options) {
        //1. 判断当前插件是否已经被安装
        if (VueRouter.install.installed) {
            return
        }
        VueRouter.install.installed = true

        //2. 把 Vue 构造函数记录到全局变量
        _Vue = Vue

        //3. 把创建 Vue 实例时候传入的 router 对象注入到 Vue 实例上
        _Vue.mixin({
            beforeCreate() {
                if (this.$options.router) {
                    _Vue.prototype.$router = this.$options.router
                    this.$options.router.init()
                }
            }
        })

    }

    init() {
        this.createRouterMap()
        this.initComponents(_Vue)
        this.initEvent()
    }

    createRouterMap() {
        // 遍历所有的路由规则，把路由规则解析成键值对的形式， 存储到routeMap中
        this.options.routes.map(route => {
            this.routeMap[route.path] = route.component
        })
    }

    initComponents(Vue) {
        Vue.component('router-link', {
            props: {
                to: String
            },
            render(h) {
                return h('a', {
                    attrs: {
                        href: '/#' + this.to
                    },
                    on: {
                        click: this.clickHandler
                    }
                }, this.$slots.default)
            },
            methods: {
                clickHandler(e) {
                    this.$router.data.currentRoute = this.to
                    window.location.href = '/#' + this.to
                    e.preventDefault()
                }
            }
        })

        const self = this
        Vue.component('router-view', {
            render(h) {
                const component = self.routeMap[self.data.currentRoute]
                return h(component)
            }
        })
    }

    initEvent() {
        window.addEventListener('hashchange', () => {
            this.data.currentRoute = window.location.hash.replace('#', '')
        })
    }
}